The present disclosure relates generally to a toner comprising a binder and at least one colorant, wherein the binder is comprised entirely of crystalline sulfonated polyester or includes crystalline sulfonated polyester along with a linear amorphous sulfonated polyester and optionally a branched sulfonated polyester. Additionally, the present exemplary embodiments relate to processes for forming such toner compositions. This disclosure finds particular application in conjunction with xerographic or electrostatographic printing processes, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications.
Xerographic toners of a resin, a pigment, and a charge control agent are known. Toners useful for xerographic applications should exhibit certain performances related to storage stability, and particle size integrity, that is, it is desired to have the particles remain intact and not agglomerate until they are fused on paper. Since environmental conditions vary, the toners also should not substantially agglomerate up to a temperature of from about 50° C. to about 55° C. The toner composite of resins and colorant should also display acceptable triboelectrification properties that vary with the type of carrier or developer composition.
Another desirable property for xerographic toner compositions to possess is fusing property on paper. Due to energy conservation measures, and more stringent energy characteristics placed on xerographic engines, such as on xerographic fusers, there is pressure to reduce the fixing temperatures of toners onto paper, such as achieving fixing temperatures of from about 90° to about 120° C., to permit less power consumption and allowing the fuser system to possess extended lifetimes. For a noncontact fuser, that is a fuser that provides heat to the toner image on paper by radiant heat, the fuser usually is not in contact with the paper and the image. For a contact fuser, that is a fuser which is in contact with the paper and the image, the toners should not substantially transfer or offset onto the fuser roller, referred to as hot or cold offset depending on whether the temperature is below the fixing temperature of the paper (cold offset), or whether the toner offsets onto a fuser roller at a temperature above the fixing temperature of the toner (hot offset).
Fixing performance of a toner can be characterized as a function of temperature. The maximum temperature at which the toner does not adhere to the fuser roll is called the hot offset temperature (HOT). When the fuser temperature exceeds HOT, some of the molten toner adheres to the fuser roll during fixing and is transferred to subsequent substrates containing developed images, resulting for example in blurred images. This undesirable phenomenon is called offsetting. Less than the HOT of the toner is the minimum fixing temperature (MFT) of the toner, which is the minimum temperature at which acceptable adhesion of the toner to the support medium occurs, that is, as determined by, for example, a crease test. The difference between MFT and HOT is called the fusing latitude of the toner, i.e., the temperature difference between the fixing temperature and the temperature at which the toner offsets onto the fuser. The fusing latitude should be as large as possible.
For oil containing fuser rolls, the toner compositions may not contain a wax. For fusers without oil on the fuser (usually hard rolls), however, the toner composites will usually contain a lubricant like a wax to provide release and stripping properties. Additionally, depending on the xerographic applications, other toner characteristics may be desired, such as providing high gloss images, especially in pictorial color applications.
Additionally, small sized toner particles, such as having average particle sizes of from about 3 to about 12 microns, and preferably from about 5 to about 7 microns, are desired, especially in xerographic engines wherein high resolution is a characteristic. Toners with the aforementioned small sizes can be economically prepared by chemical processes, which involves the direct conversion of emulsion sized particles to toner composites by aggregation and coalescence, or by suspension, microsuspension or microencapsulation processes.
Low fixing toners comprised of semicrystalline resins are known, such as those disclosed in U.S. Pat. No. 5,166,026, and wherein toners comprised of a semicrystalline copolymer resin, such as poly(alpha-olefin) copolymer resins, with a melting point of from about 30° C. to about 100° C., and containing functional groups comprising hydroxy, carboxy, amino, amido, ammonium or halo, and pigment particles, are disclosed. Similarly, in U.S. Pat. No. 4,952,477, toner compositions comprised of resin particles selected from the group consisting of semicrystalline polyolefin and copolymers thereof with a melting point of from about 50° C. to about 100° C., and containing functional groups comprising hydroxy, carboxy, amino, amido, ammonium or halo, and pigment particles, are disclosed. Although, it is indicated that some of these toners may provide low fixing temperatures of about 200° F. to about 225° F. using contact fusing applications, the resins are derived from components with melting characteristics of about 30° C. to about 50° C., and which resins are not believed to exhibit more desirable melting characteristics, such as about 55° C. to about 60° C.
In U.S. Pat. No. 4,990,424, toners comprised of a blend of resin particles containing styrene polymers or polyesters, and components selected from the group consisting of semicrystalline polyolefin and copolymers thereof with a melting point of from about 50° C. to about 100° C. are disclosed. Fusing temperatures of from about 250° F. to about 330° F. are reported.
Low fixing crystalline based toners are disclosed in U.S. Pat. No. 6,413,691, and wherein a toner comprised of a binder resin and a colorant, the binder resin containing a crystalline polyester containing a carboxylic acid of two or more valences having a sulfonic acid group as a monomer component, are illustrated. The crystalline resins of the '691 patent are believed to be opaque, resulting in low projection efficiency.
Crystalline based toners are disclosed in U.S. Pat. No. 4,254,207. Low fixing toners comprised of crosslinked crystalline resin and amorphous polyester resin are illustrated in U.S. Pat. No. 5,147,747 and U.S. Pat. No. 5,057,392, and wherein the toner powder is comprised, for example, of polymer particles of partially carboxylated crystalline polyester and partially carboxylated amorphous polyester that has been crosslinked together at elevated temperature with the aid of an epoxy novolac resin and a crosslinking catalyst.
U.S. Pat. No. 5,916,725 describes a process for the preparation of toner comprising mixing an amine, an emulsion latex containing sulfonated polyester resin, and a colorant dispersion, heating the resulting mixture, and optionally cooling.
Illustrated in U.S. Pat. No. 5,593,807, the disclosure of which is totally incorporated herein by reference in its entirety, is a process for the preparation of toner compositions comprising, for example, (i) preparing an emulsion latex comprised of sodio sulfonated polyester resin particles of from about 5 to about 500 nanometers in size diameter by heating the resin in water at a temperature of from about 65° C. to about 90° C.; (ii) preparing a pigment dispersion in water by dispersing in water from about 10 to about 25 weight percent of sodio sulfonated polyester and from about 1 to about 5 weight percent of pigment; (iii) adding the pigment dispersion to the latex mixture with shearing, followed by the addition of an alkali halide in water until aggregation results as indicated, for example, by an increase in the latex viscosity of from about 2 centipoise to about 100 centipoise; (iv) heating the resulting mixture at a temperature of from about 45° C. to about 55° C. thereby causing further aggregation and enabling coalescence, resulting in toner particles of from about 4 to about 9 microns in volume average diameter and with a geometric distribution of less than about 1.3; and optionally (v) cooling the product mixture to about 25° C. and followed by washing and drying. The sulfonated polyesters of this patent may be selected for use in embodiments of the present invention.
Emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,346,797, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797.
There is thus a need to provide super low melt and ultra low melt toners that may be used at lower fusing temperatures and that still provide excellent image properties. There is thus also a need to provide a process for preparing such low melt emulsion aggregation toners that allows for controlled particle growth and controlled morphology or shape, and provides high yields.